1. Field of the Invention
The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus characterized by a technique for fixing an image pickup element within a barrel.
2. Description of the Related Art
An electronic still camera, i.e. a so-called digital camera, which converts an object image formed by a photographic optical system into an electric signal using an image pickup element, such as a CCD or a MOS are in widespread use. Some of the image pickup elements, such as a CCD and a MOS, are sensitive to infrared light invisible to the human eye, and hence, some digital cameras have an infrared ray cut filter provided in its photographic optical system so as to prevent degradation of image quality due to infrared light.
Further, some image pickup apparatuses have an optical low-pass filter made of a crystal exhibiting birefringent phenomenon and disposed on the object-side front surface of an image pickup element so as to prevent degradation of image quality due to false colors or moire caused by picking up an image of an object containing a sampling frequency dependent on the pixel pitch of the image pickup element.
The infrared ray cut filter or optical low-pass filter (hereinafter referred to as “the optical filter component”), or both of them are held by a base plate formed with an opening for passing photographic optical flux therethrough and a recess for positioning the optical filter component without large displacement. More specifically, the optical filter component is held by being fitted and glued in the base plate.
By the way, when dust adheres to the surface of an image pickup element, light is not admitted through a portion where the dust is adhering, and hence the image of the dust is captured as a shadow in an object image, and the image of the shadow is formed in a picked-up image. Further, an image pickup element is generally located inward of a shooting lens, and hence it is impossible for the user to clean the image pickup element. Therefore, in order to avoid picking up the image of dust, the image pickup apparatus is required to have a structure that makes it possible to prevent dust from adhering to the image pickup element. For this reason, the image pickup element generally has a front surface thereof covered by a protective glass.
However, when a large piece of dust adheres to the protective glass, the image of the dust can be picked up. To solve this problem, there has been proposed an image pickup apparatus in which a space between an optical filter component and a protective glass is hermetically sealed so as to prevent dust from adhering to the protective glass.
Furthermore, a mechanism for performing fine adjustment of the position and attitude of an imaging surface is sometimes required so as to accommodate manufacturing errors of the photographic optical system. Improvement of assemblability of the optical filter component and the image pickup element is always required for reduction of assembling costs. In addition, the thickness of the optical system in the optical axis direction should be smaller so as to enhance the portability of the image pickup apparatus.
Conventionally, in order to reduce thickness of a structure of an optical filter component and a protective glass with a space therebetween hermetically sealed, in the direction of the optical axial of the optical system, there have been proposed various mechanisms for holding the image pickup element and the optical filter component in a barrel.
For example, in a technique disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2006-67356, a low-pass filter holder formed by a metal member in the form of a thin plate for holding the optical filter component is provided so as to reduce the thickness of the optical system in the optical axis direction. Further, in a technique disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-12334, the optical filter component and the image pickup element are held by being rigidly glued to each other.
Japanese Laid-Open Patent Publication (Kokai) No. 2006-67356 mentioned above discloses a construction in which the optical filter component held in the low-pass filter holder has an elastic member provided thereunder and the elastic member is sandwiched between the image pickup element and the optical filter component. However, in the case of this construction, excessive pressure can be applied to the optical filter component depending on variation in the thickness of the optical filter component, thereby causing failure of the optical filter component.
On the other hand, in the technique disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-12334, the optical filter component and the image pickup element are glued to each other, and hence it is required to hold the optical filter component until an adhesive is cured, which degrades the assemblability. Further, it is difficult to separate the optical filter component and the image pickup element, and hence when one of the two components fails, the other component, which is normal, has to be disposed of as junk.
Furthermore, neither of Japanese Laid-Open Patent Publications (Kokai) No. 2006-67356 and No. 2005-12334 permit adjustment of the position of the image pickup surface in the optical axis direction nor the inclination of the same with respect to the optical axis.